Process controls are used in the semiconductor manufacturing world. Semiconductor devices are formed by a multitude of processing operations carried out upon a semiconductor or other substrate and each of the processing operations must be well controlled. The processing operations should exhibit run-to-run uniformity, i.e. process repeatability, and uniformity across the substrate being processed for each run. This is especially true in today's rapidly advancing semiconductor manufacturing industry in which device feature sizes are becoming smaller, the substrates upon which semiconductor devices are formed are becoming larger and a greater number of processing operations are used to form the semiconductor devices that are increasing in complexity. It is important for the millions of features that are simultaneously formed across the substrate to have the same dimensions and characteristics throughout the substrate each time a processing operation, i.e. run, is carried out.
This applies to various different types of processing operations such as thermal operations, deposition operations, coating operations, implantation operations, etching operations, epitaxial growth operations, polishing operations and various other operations used in semiconductor manufacturing.
It would therefore be advantageous to provide useful and reliable statistical process control techniques and methods.